A motor vehicle anti-lock braking system (referred to herein as an ABS system) repeatedly releases and re-applies hydraulic brake pressures during conditions of wheel lock with the objective of maximizing the tractive force between the vehicle tires and the road surface. However, the control strategies assume that the brake system is operating normally, and the system performs at a sub-optimal level when the braking effectiveness is degraded due to fluid leakage, fading, poor adjustment, wear, and so forth. Accordingly, what is needed is an anti-lock brake control method that adaptively compensates for degraded braking effectiveness.